IO::Handle - supply object methods for I/O handles
- use IO::Handle;
- $io = IO::Handle->new();
- if ($io->fdopen(fileno(STDIN),"r")) {
- print $io->getline;
- $io->close;
- }
- $io = IO::Handle->new();
- if ($io->fdopen(fileno(STDOUT),"w")) {
- $io->print("Some text\n");
- }
- # setvbuf is not available by default on Perls 5.8.0 and later.
- use IO::Handle '_IOLBF';
- $io->setvbuf($buffer_var, _IOLBF, 1024);
- undef $io; # automatically closes the file if it's open
- autoflush STDOUT 1;
IO::Handle
is the base class for all other IO handle classes. It is
not intended that objects of IO::Handle
would be created directly,
but instead IO::Handle
is inherited from by several other classes
in the IO hierarchy.
If you are reading this documentation, looking for a replacement for
the FileHandle
package, then I suggest you read the documentation
for IO::File
too.
Creates a new IO::Handle
object.
Creates an IO::Handle
like new
does.
It requires two parameters, which are passed to the method fdopen
;
if the fdopen fails, the object is destroyed. Otherwise, it is returned
to the caller.
See perlfunc for complete descriptions of each of the following
supported IO::Handle
methods, which are just front ends for the
corresponding built-in functions:
- $io->close
- $io->eof
- $io->fcntl( FUNCTION, SCALAR )
- $io->fileno
- $io->format_write( [FORMAT_NAME] )
- $io->getc
- $io->ioctl( FUNCTION, SCALAR )
- $io->read ( BUF, LEN, [OFFSET] )
- $io->print ( ARGS )
- $io->printf ( FMT, [ARGS] )
- $io->say ( ARGS )
- $io->stat
- $io->sysread ( BUF, LEN, [OFFSET] )
- $io->syswrite ( BUF, [LEN, [OFFSET]] )
- $io->truncate ( LEN )
See perlvar for complete descriptions of each of the following
supported IO::Handle
methods. All of them return the previous
value of the attribute and takes an optional single argument that when
given will set the value. If no argument is given the previous value
is unchanged (except for $io->autoflush will actually turn ON
autoflush by default).
- $io->autoflush ( [BOOL] ) $|
- $io->format_page_number( [NUM] ) $%
- $io->format_lines_per_page( [NUM] ) $=
- $io->format_lines_left( [NUM] ) $-
- $io->format_name( [STR] ) $~
- $io->format_top_name( [STR] ) $^
- $io->input_line_number( [NUM]) $.
The following methods are not supported on a per-filehandle basis.
- IO::Handle->format_line_break_characters( [STR] ) $:
- IO::Handle->format_formfeed( [STR]) $^L
- IO::Handle->output_field_separator( [STR] ) $,
- IO::Handle->output_record_separator( [STR] ) $\
- IO::Handle->input_record_separator( [STR] ) $/
Furthermore, for doing normal I/O you might need these:
fdopen
is like an ordinary open except that its first parameter
is not a filename but rather a file handle name, an IO::Handle object,
or a file descriptor number. (For the documentation of the open
method, see IO::File.)
Returns true if the object is currently a valid file descriptor, false otherwise.
This works like <$io> described in I/O Operators in perlop
except that it's more readable and can be safely called in a
list context but still returns just one line. If used as the conditional
within a while
or C-style for
loop, however, you will need to
emulate the functionality of <$io> with defined($_ = $io->getline)
.
This works like <$io> when called in a list context to read all the remaining lines in a file, except that it's more readable. It will also croak() if accidentally called in a scalar context.
Pushes a character with the given ordinal value back onto the given handle's input stream. Only one character of pushback per handle is guaranteed.
This write is somewhat like write found in C, in that it is the
opposite of read. The wrapper for the perl write function is
called format_write
. However, whilst the C write function returns
the number of bytes written, this write function simply returns true
if successful (like print). A more C-like write is syswrite
(see above).
Returns a true value if the given handle has experienced any errors
since it was opened or since the last call to clearerr
, or if the
handle is invalid. It only returns false for a valid handle with no
outstanding errors.
Clear the given handle's error indicator. Returns -1 if the handle is invalid, 0 otherwise.
sync
synchronizes a file's in-memory state with that on the
physical medium. sync
does not operate at the perlio api level, but
operates on the file descriptor (similar to sysread, sysseek and
systell). This means that any data held at the perlio api level will not
be synchronized. To synchronize data that is buffered at the perlio api
level you must use the flush method. sync
is not implemented on all
platforms. Returns "0 but true" on success, undef on error, undef
for an invalid handle. See fsync(3c).
flush
causes perl to flush any buffered data at the perlio api level.
Any unread data in the buffer will be discarded, and any unwritten data
will be written to the underlying file descriptor. Returns "0 but true"
on success, undef on error.
Turns on autoflush, print ARGS and then restores the autoflush status of the
IO::Handle
object. Returns the return value from print.
If called with an argument blocking
will turn on non-blocking IO if
BOOL
is false, and turn it off if BOOL
is true.
blocking
will return the value of the previous setting, or the
current setting if BOOL
is not given.
If an error occurs blocking
will return undef and $!
will be set.
If the C functions setbuf() and/or setvbuf() are available, then
IO::Handle::setbuf
and IO::Handle::setvbuf
set the buffering
policy for an IO::Handle. The calling sequences for the Perl functions
are the same as their C counterparts--including the constants _IOFBF
,
_IOLBF
, and _IONBF
for setvbuf()--except that the buffer parameter
specifies a scalar variable to use as a buffer. You should only
change the buffer before any I/O, or immediately after calling flush.
WARNING: The IO::Handle::setvbuf() is not available by default on Perls 5.8.0 and later because setvbuf() is rather specific to using the stdio library, while Perl prefers the new perlio subsystem instead.
WARNING: A variable used as a buffer by setbuf
or setvbuf
must not
be modified in any way until the IO::Handle is closed or setbuf
or
setvbuf
is called again, or memory corruption may result! Remember that
the order of global destruction is undefined, so even if your buffer
variable remains in scope until program termination, it may be undefined
before the file IO::Handle is closed. Note that you need to import the
constants _IOFBF
, _IOLBF
, and _IONBF
explicitly. Like C, setbuf
returns nothing. setvbuf returns "0 but true", on success, undef on
failure.
Lastly, there is a special method for working under -T and setuid/gid scripts:
Marks the object as taint-clean, and as such data read from it will also be considered taint-clean. Note that this is a very trusting action to take, and appropriate consideration for the data source and potential vulnerability should be kept in mind. Returns 0 on success, -1 if setting the taint-clean flag failed. (eg invalid handle)
An IO::Handle
object is a reference to a symbol/GLOB reference (see
the Symbol
package). Some modules that
inherit from IO::Handle
may want to keep object related variables
in the hash table part of the GLOB. In an attempt to prevent modules
trampling on each other I propose the that any such module should prefix
its variables with its own name separated by _'s. For example the IO::Socket
module keeps a timeout
variable in 'io_socket_timeout'.
perlfunc, I/O Operators in perlop, IO::File
Due to backwards compatibility, all filehandles resemble objects
of class IO::Handle
, or actually classes derived from that class.
They actually aren't. Which means you can't derive your own
class from IO::Handle
and inherit those methods.
Derived from FileHandle.pm by Graham Barr <gbarr@pobox.com>